Various aircraft passenger crash survival systems are known. For fixed-wing aircraft, ejector systems are often employed and serve to eject a passenger from an aircraft prior to its crashing.
For helicopters and similar types of vertical takeoff aircraft, ejector systems, which are operative to eject a passenger from the aircraft in a generally upward direction, are generally combined with additional safety systems to prevent serious injury from the rotor blades to a person being ejected. It has been found that such systems, which include means for prior severance of the rotor blades, are very expensive.
As an aircraft crashes in a direction substantially parallel to the direction of gravitational acceleration, for a very short time after it has come to rest, passenger seats therein continue to travel downwards. In a case wherein the passenger does not leave the aircraft prior to its crashing, a reduction in the force transferred to the passenger would cause a corresponding reduction in the degree of injury that would otherwise be sustained by him.
Various energy absorbing systems have, therefore, been developed to reduce the force of an impact that would otherwise be transferred to a passenger in a vertical takeoff aircraft crash.
Several aircraft crash survival systems are documented in the Oct./Nov. 1986 issue of DEFENCE HELICOPTER WORLD, in an article entitled "Take Your Seat" by George Marsh.
In a typical crash situation, a vertical takeoff aircraft may fall from a height of 15-30 m with an acceleration upon impact of about 60-100 g. The aircraft may be expected to dissipate up to about 50% of the crash energy through the landing gear while approximately an additional 15% of the remainder will be dissipated through the controlled crash of the fuselage structure. The remaining crash energy should, therefore, ideally be absorbed by the passenger seat.
To illustrate the importance of dissipating crash energy before it is transferred to the passenger, it is noted that very severe spinal fractures have been found to be caused at approximately 30 g, while at about 40 g death is to be expected due to damage to both the spinal column and to the cardiovascular system. It has further been found that an acceleration of about 13.5 g is sustainable by the spinal column without causing irreversible damage thereto.
Disclosed in U.S. Pat. No. 4,523,730 to Martin is an energy absorbing seat arrangement, particularly for a helicopter, in which a seat pan is carried by a frame slidably mounted on parallel upwardly extending pillars secured to the helicopter. In normal conditions, downwards sliding of the frame on the pillars is prevented, in one embodiment, by metal rods fixed with respect to the pillars, and extending through drawing dies fixed with respect to the seat frame. In a variant the rods and dies are replaced by a deformable metal tube and a mandrel extending through the tube.
In the event of a crash in which rapid downward movement of the helicopter and the pillars is halted suddenly, the seat and seat frame continue to move downwardly, sliding along the pillars, while drawings of the rods through the dies, or of the mandrel through the tube, to dissipate the kinetic energy of the seat and its occupant relatively gradually.
The seat arrangement to Martin has a number of disadvantages, among which is the massiveness of its construction and its consequent weight. This is characterized by the presence of one assembly for permitting downward travel of the seat and another assembly, for absorbing crash energy in either of the ways described above. Typically, the seat to Martin has a weight of no less than about 15 kg.
A further disadvantage of Martin's seat is the lack of any apparatus for preventing rebound once the seat has completed a downward stroke.
Also available is a crashworthy seat for helicopter pilots and copilots using the `Tor-Shok energy absorbing system` and manufactured by Aerospace Research Associates Inc., of 2017 West Garvey Ave., West Covinia, Calif. 91790, U.S.A..
In addition, available from Services Commerciaux et Antenne Technique of 16, rue Franklin, 75016, Paris, France are helicopter crashworthy seats for pilots, copilots and troops.
A disadvantage of `crashworthy` seats in general is that they are generally not foldable and, therefore, when not in use, they take up potentially valuable cargo space within an aircraft.